Steam generating and superheating unit



Feb. 13, 1962 ROWAND 3,020,894

STEAM GENERATING AND SUPERHEATING UNIT LOW PR ESS U RE STEAM OU TLET INVENTOR. Will H. Rowand BY FIGI [I ATTORNEY Feb. 13, 1962 w. H. ROWAND STEAM GENERATING AND SUPERHEATING UNIT 8 Sheets-Sheet 2 Filed NOV. 1, 1955 INVENTOR. Will H. Rowand TH T5 HHL J (HHHHHH LOW PRESSURE STEAM OUTLET HH! M MI-HI FIG 2 ATTORNEY Feb. 13, 1962 w. H. ROWAND STEAM GENERATING AND SUPERHEATING UNIT 8 Sheets-Sheet 3 Filed Nov. 1, 1955 IQOq m o a m l 6 5 I f 6 m\ vmmmm\ k a \VQ X 5 00000) 90000) K 8888, 88 a 000000 000000 000000 0.0000 0 2308 8003 g 9888 m\ cocoon cocoon 2 8888 B880 6 00080 eooooo 000000 000000 u gonna oooooo an 80000 000000 5. 89 80 ocoooo oooooo oooooc 03000 0 4 23000 000000 833% n n 6 caoooo cocoon 0 000000 000000 000000 ocooooll 3 4 80880 L8888o oooooooooaoaag M 9 4 000000 000000 0 000000 000000 000000 000000 0 000000 000000 8 000000 25000 c 7 nooooo 02300 8888 B888 4 D000 000000 ca 8888 8.8080 5 aooooo 000000 R 2 000000 00250 7 000000 00080 H n n o oooooa 00008 a R 000000 000000 economy oooooo E0 00000 00000 wwq w \C @HQ 6 x 6 O 8 O m M 6 7 I FIG 3 INVENTOR. Will H. Rowand ATTORNEY Feb. 13, 1962 w, H. ROWAND 3,020,894

STEAM GENERATING AND SUPERHEATING UNIT Filed Nov. 1, 1955 HIGH PRESS. 94 STM. SOURCE 260 INVENTOR.

Will H. Rowand 24a BY ATTORNEY Feb. 13, 1962 w. H. ROWAND STEAM GENERATING AND SUPERHEATING UNIT 8 Sheets-Sheet 5 Filed Nov. 1, 1955 INVENTOR.

Will H. Rowand FIG 5 ATTOR NEY Feb. 13, 1962 w. H. ROWAND STEAM GENERATING AND SUPERHEATING UNIT 8 Sheets-Sheet 6 Filed Nov. 1, 1955 IQOi:

O 06 00000000 00000000 880000 I|I| 7 0 0 00000000 00000000 8000000 4 03 00000000 00000000 80088 0 60000000 00000000 5 0 000000000000000002 8000000 O O O O 0/4 aooooooomoooooooum 908000 00 OUODOODD 00000090 g o 3 UOOQOOOO OQODOOOD 5 ll 8 0 50000000 00000000 Q88 G 0 00000000 DOODOODO g o 0 00800050 OODOOOOO E28 w 3 0 6 00000000 00000000 808%380 00 OOQOOOOO 00000000 885 n 0 00000000 00000000 5 0 252K 83 1 o o o o 0 00000000 00000000/ 00000000 Fl 0 00000000 00000000 80808 0 00000000 QOOOQOOO 880g 0 00000000 00000000 8000000 l||| 0 00000000 00000000 50080 O O OOOOO2QQO4 g 2 0 2.000000 00000000 3 088000 8 2 2 0 00000000 00000000 00880 4 2 0 00000o0-0\ 00000000 0600000 4 6 0 0000000 OOQDOOQ n 4 N N Y \\\\1|l|il|l|# |1l||| 4 i V 4 J 8 8 O O 5 3 6 4 43 4 2 FIG 6 INVENTOR. Will H. Rowand ATTORNEY United States Patent Ofii ce is 3,020,894 Patented Feb. 13, 1962 3,020,894 STEAM GENERATING AND SUPER- HEATING UNIT Will H. Rowand, Short Hills, N.J., assignor to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Nov. 1, 1955, Ser. No. 544,192 2 Claims. (Cl. 122-33) This invention relates to the art of steam generation. More particularly, the invention relates to the high temperature superheating of different steam streams at different pressures and derived from different sources, at least one of which has such characteristics that it can deliver only steam at a comparatively low pressure. An example of such a source of low pressure steam is one type of a nuclear steam generating unit.

The invention is exemplified in a steam generating and superheating unit in which the steam from the low pressure source is superheated in a plural stage separately fired superheater. generating unit in which high pressure steam is generated predominantly in the wall tubes of a fuel fired furnace. Saturated steam from this high pressure (Le. 2400 p.s.i.a.) steam generating unit transmits heat by indirect heat exchange to the low pressure steam, to superheat the latter in the first stage of superheating, the high pressure steam being condensed in this first superheating stage.

The low pressure steam heated in the first superheating stage then passes through a second stage of superheating subject to the heat of high temperature heating gases of the high pressure steam unit. The low pressure steam is thus superheated in the two separate superheating stages to temperatures of the order of 1100 degrees F. Condensate resulting from the first stage of heating of the low pressure steam by indirect heat exchange from the high pressure steam, returns to the fluid system of the high pressure unit which may involve a natural circulation system which is predominantly, or wholly, condensing.

In one aspect, the invention may be regarded as a separately fired superheater burning a fossil fuel or a slag forming fuel at combustion temperatures in excess of 2200 F and having a high capacity for superheating relatively low pressure steam. When a separately fired superheater burns coal at the pertinent high temperatures, the use of high temperature non-metallic refractory materials in the manufacture of the walls of the furnace chamber of the superheater increases the cost of wall maintenance beyond allowable limits, and likewise decreases the availability of the separately fired superheater beyond the allowable limits. The separately fired superheater of this invention is characterized by high availability and low furnace chamber wall maintenance by reason of its inclusion in the furnace chamber walls adjacent the active combustion zone of vapor generating tubes operating at the saturation temperature of a high pressure vapor, while the wall portions of the furnace chamber beyond the active combustion zone in a gas flow sense contain radiant superheater wall tubes forming the secondary superheater, receiving low pressure steam from an independent heating source. The separately fired superheater of the invention also involves an indirect heat exchanger presenting the primary superheater for the low pressure steam which is superheated in the primary superheater stage by heat transfer from the high pressure steam in indirect heat exchange relationship, the high pressure steam, being condensed in the primary superheating stage and returned to the inlets of the steam generating tube bounding the zone of active combustion. In one modification of the pertinent separately fired superheater there is a vertically elongated furnace chamber with the steam generating wall The latter includes a high pressure steam tubes limited to the lower and minor part of the chamber, the remainder and major parts of the walls of the furnace chamber including radiant superheater wall tubes.

The invention will be clearly and concisely set forth in the claims appended hereto, but for a more complete un derstanding of the invention, its advantages and uses, reference should be had to the following description which refers to the attached drawings, showing preferred embodiments of the apparatus involved in the invention.

In the drawings:

FIG. 1 is a diagramamtic sectional elevation indicating the high pressure condensing steam generating unit coordinated with, and effecting, the plural stage superheating of low pressure steam;

FIG. 2 is a vertical section transverse to the plane of FIG. 1 and taken on the sectional line 2-2 of FIG. 1, looking in the direction of the associated arrows;

FIG. 3 is a plan section on the line 3-3 of FIG. 1;

'FIG. 4 is a sectional side elevation of a modified separately fired superheater unit incorporating the principles of the invention;

FIG. 5 is a vertical section on the section line 55 of FIG. 4, and looking in the direction of the arrows;

FIG. 6 is a plan section on the line 66 of FIG. 4;

FIG. 7 is a fragmentary sectional side elevation primarily illustrating the separate superheating circuit for the low pressure steam, taken on the vertical plane of the section line 77 of FIG. 6; and

FIG. 8 is a plan schematically showing the relationship of the superheater headers for the low pressure steam superheating circuit and for the high pressure steam superheating circuit.

Referring now to FIG. 1 of the drawings, low pressure steam as from such an independent source as a nuclear steam generating power plant passes to the inlet 10 of the first superheating stage. Here the steam is superheated by indirect heat transfer in a heat exchanger 12, a plurality of which may be employed as indicated at 1215 at the upper part of FIG. 2. The heat exchanger 12 receives, through the conduit 18, high pressure steam from the steam and water drum 20 of the high pressure steam generating unit. This high pressure steam passes to the inlet chamber 22 of the heat exchanger 12, and then through a plurality of spaced tubes 24, the inlets of which communicate with the high pressure steam inlet 22. The outlets of these tubes, fixed within the tube sheet 26, communicate with the intermediate high pressure steam chamber 28 from which the high pressure steam passes through a series of spaced tubes 30 to the high pressure steam outlet chamber 32 of the heat exchanger. Normally, the effluent of these tubes passing into the chamber 32 is predominantly condensate, which is then returned through the conduits 34 to the steam and water drum 20, or other condensate or liquid space of the high pressure steam generating unit.

The tubes 24 and 30 are disposed within a hollow cylindrical shell 36 which receives low pressure steam through the inlet 10. This low pressure steam is partially superheated in the heat exchanger 12 from which it is conducted through tubes 38 and 40 to the second superheating stage. As well understood in the art, the shell 36 of the heat exchanger 12 is in pressure tight relationship with the tube sheet 26 and its companion tube sheet 41 at the steam inlet end of the heat exchanger. The superheated steam conducting tubes 40 have their outlets 42 communicating with the upright header 44 disposed at the upper part of and along the wall of the high pressure steam generator, including the water wall furnace 46 fired by the fuel burners 48.

The remainder of the superheated steam from the first stage of superheating of low pressure steam passes through the tubes or conduits 38 to the horizontal header 50, the

superheated steam from the first superheating stage thus passing through two paths of flow through the second superheating stage. Considering the first path of flow as leading from the upright header 44, the steam passes from this header through two upright rows 52 and 54 (FIG. 3) of contiguously arranged and horizontally disposed wall tubes. The tubes 52 extend along the wall section 56 to the side wall 58 where they continue through their similarly disposed sections 60 to a position at the rear wall of the superheating gas space of the high temperature steam generating unit, from which point the steam flow continues through the final sections of these tubes 62, to the upright intermediate header 64. Similarly, the tubes 54 extend along the wall section 66 and then through sections 68, arranged along the wall 70. The steam flow then further continues through the rear wall tube section 72 to the header 64.

From the header 64 the steam flow continues through one or more conduits, such as indicated at 74 in FIG. 1 to the mixing header 76.

Now referring to the other path of flow of the low pressure superheated steam through the second superheating stage, this fiow proceeds from the header 50 through the roof tubes 75. These tubes continue through their sections 77 along the roof of the gas pass leading from the furnace 46. The steam flow in these tubes then continues through the upright tube sections 78 and thence through the horizontal sections 80 extending along the floor of the gas pass 82, and having their outlet ends communicating with the header 84. From this header the steam is conducted by one or more conduits 86 to the mixing header 76.

The superheated steam flows from the above described flow paths are mixed within the header 76, the combined steam then flowing through the banks of vertically disposed and horizontally spaced banks of tubes 90-93 of the secondary superheater. These banks of tubes, as indicated in FIG. 1, are formed by return bend tubular sections connected for series flow of steam therethrough.

The banks of tubes 90-93 are spaced from each other in the direction of gas fiow as indicated in FIG. 1 of the drawings, the outlets of the first bank of secondary superheater tubes 90 being joined by the tubular connections 96 to the inlets of the return bend tubes constituting the bank of tubes 91. Similarly the steam fiow from the outlets of the return bend tubes constituting the bank of tubes 91 continues through the horizontal connecting tubular sections 98 to the inlets of the return bend tubes constituting the bank of tubes 93. From the outlets of these return bend tubes the steam fiows through the connecting tubular sections 100 to the inlets of the return bend tubes constituting the bank of tubes 92. In the outlet portions of these last mentioned return bend tubes the steam flows upwardly between the rows of the tubular connectors 98, and through the roof of the high pressure steam generating unit as indicated at 102. These tubes communicate with the header 106, from which the highly superheated low pressure steam passes through a low pressure stage of a multiple stage steam turbine, or to another appropriate point of use.

The high pressure steam generating unit of FIG. 1 is indicated as a natural circulation unit including the large diameter downcomers 110 leading from the water or liquid space of the drum 20 to positions at the lower part of the unit where the downcomers are connected by the circulators, such at 112, 114, 116 passing to their associated headers, some of which are illustrated at 119-122.

The unit shown in FIG. 1 is a hopper bottom unit with the steam generating tubes leading upwardly from the headers 121 and 122, having lower sections 126 and 128 arranged along the upwardly diverging hopper walls at the lower part of the unit. Some of the tubes 126 continue upwardly along the wall 130 of the furnace 46, past the burners 48 and directly upwardly to the header 132. The upper portions of these tubes are preferably widely spaced across the inlet of the gas pass 82 leading from the upper part of the high temperature gas chamber of the high pressure generating unit. The fluid flow from the header 132 continues through the circulators 134 to the mixture inlet space of the drum 20, from which the mixture is delivered to appropriate steam and water separators in order that the separated steam may flow through the conduits 18 to the indirect heat exchangers of the first stage of superheating and in order that the separated water may continue its circulatory flow downwardly into the lower part of the drum and thence through the downcomers 110. Others of the tubes leading upwardly along the furnace wall have the arch portions 136 delineating an arch extending into the furnace 46 at a position just below the entrance to the gas pass 82. The outlets of these tubes communicate with the header 138 from which the fluid flows through the upright circulators 140 to the side wall headers 142. From these headers appropriate circulators 144 communicate with the mixture space of the steam and water drum 20 in the manner above indicated with reference to the circulators 134. Along the opposite wall of the furnace 46 the tubes leading upwardly from the header 122 have the furnace sections 146 contiguously or closely arranged to receive heat predominantly radiantly from the high temperature gases within the furnace 46 for the generation of steam. Some of these tubes 146 continue upwardly past the header 148 without communication therewith as clearly indicated at 150 in FIG. 1. Others of the tubes 146 communicate with the header 148. From this header other tubes extend upwardly along the furnace wall sections 56 and 66 (FIG. 3) to constitute the superheater tube supporting sections 152, appropriate superheater tube supporting devices being secured to the upright sections 152 to maintain the superheater tubes sections 52 and 54 (FIG. 3) in their operative relationships. The outlet ends of these upright tubular sections 152 communicate directly with the header section 154, and thence through the circulators 156 with the mixture space of the steam and water drum 20.

FIG. 1 indicates a similar arrangement of wall tube sections along the side wall 70 of the furnace. The furnace tubes along this wall are facing the observer in FIG. 1. These side wall tubes include a group of contiguously or closely arranged tubes 160 leading upwardly from the header 119, and a similar group 162 leading upwardly from the header 120. Between the headers 119 and 120, and at a lower position at a level near the level of the headers 121 and 122 there is an intervening side wall header 163 connected to the downcomers 110 by the circulators 114, and connected to steam generating tubes leading upwardly along the furnace wall at an intermediate zone, as indicated at 164. Some of the furnace wall tubes of the groups 160, 162 and 164 continue upwardly past the header 166 without communication therewith. Others of these tubes communicate with a horizontal header section 166 disposed at the level of the header section 148. From this header other tubes extend upwardly along the furnace wall section 70 (FIG. 3) to constitute the superheater supporting sections 170. From this header these widely spaced superheater support risers 170 pass upwardly in contiguous relation to the wall of superheater tube sections 68, and have their outlets connected to the side wall header 172. This header is connected through risers 144 with the mixture space of the drum 20. It is to be understood that there is a similar arrangement of tubular sections, headers, and risers along each of the opposite walls 70 and 58.

The pulverized coal burners 48 of the high pressure steam generating unit are disposed within a windbox 180, which receives high temperature air through the ductwork 182 from the air outlet of the air heater 184, the latter being heated by the heating gases of the high pressure steam generating unit passing downwardly through the duct 186 from the gas outlet of the gas pass 82.

The pressure parts and other components of the unit are appropriately supported by steel work including uprights, such as those indicated at 190 and 192, and connecting beams such as indicated at 194, 196 and 198 in FIG. 1. Other components of this steel work are indicated at 196 and 198 in FIG. 2.

The invention also includes a modified type of steam generating and superheating system such as illustrated in FIGS. 4 to 8 of the drawings. This modified system involves a coal fired, separately fired superheater, the latter having separate superheater systems one of which receives low pressure steam at a pressure of the order of 350 p.s.i. and the other receiving steam at a pressure of the order of 600 p.s.i. Thus this modified type of unit is adapted to cooperate with a dual cycle water nuclear reactor system. The modified unit incorporates a water wall section including the fuel burning zone of a cyclone furnace and its associated primary furnace chamber. This water wall section is a part of a natural circulation steam generating component operating at a pressure of the order of 2400 p.s.i. The steam generated in this section passes to heat exchangers of the feed water type wherein the heat from the condensation of the high pressure steam is transmitted to the initial parts of two separate superheating circuits, one for high pressure steam and the other for low pressure steam coming from a source such as, for example, a nuclear reactor. This permits the elimination of the need for a refractory furnace for coal firing, and also eliminates the necessity of using steam superheater tubes in heat absorption zones of high temperature such as the zone of the cyclone furnace or the primary furnace chamber.

The modified unit as shown in FIGURE 4 of the drawings includes a coal fired cycline furnace 200 preferably of the type shown in the patent of Kerr et al. 2,594,312 of April 29, 1952. High temperature furnace gases pass from the cyclone furnace 200 through its throat 202 into the primary furnace chamber 204 and thence across the screen tubes 206 into the secondary furnace chamber 208, the Walls of the cyclone furnace and both furnace chambers including fluid heating tubes.

Above the level 210210 the walls, such as the walls 212 and 214 of the secondary furnace chamber 208 are lined with radiant superheater tubes having their inlet ends connected to header means such as indicated at 216 and 218. The radiant superheater wall tubes along the walls 212 and 214 are indicated at 220 and 222, the latter tubes having their upper parts disposed as the screen tube sections 224 and 226 widely spaced across the gas flow from the upper part of the secondary furnace chamber into and through the horizontal gas pass 228. The radiant superheater wall tubes 220 along the opposite secondary furnace chamber wall 212 have their upper parts disposed as the furnace chamber roof tube sections 230.

Below the level 210-210 the walls of the primary furnace chamber 204 and the lower part of the secondary furnace chamber 208 include steam generating tubes having their inlet ends connected to the lower header or drum 246 and their upper ends connected to header means such as 248 and 250 which, in turn, are appropriately connected as by one or more risers 252 with the steam and water inlet space of the drum 254. In the drum 254 the incoming mixtures of steam and water are subject to the fluid separating action of steam and water separators preferably of the type shown in the patent of Rowand et al. 2,289,970 of July 14, 1942, and the separated water passes through large diameter downcomers 256 to the lower drum or header 246.

The lower headers for the cyclone, such as the header 258, have circulators 260 directly connecting the headers with the header or drum 246, and it is to be understood that the tubes forming parts of the walls of the cyclone furnace 200 have their outlet ends connected to one or more headers such as 261, the latter being directly ture receiving space of the drum 254.

The floor 263 of the primary furnace chamber 204 includes the floor tube sections 264 of some of the steam generating tubes leading directly from the header 246 along the floor and then along the wall component 266 of the primary furnace chamber. Thence these tubes 'lead through the wall of the throat 202 and then through the wall component 268 of the primary furnace chamber. Other tubes directly connecting the header 246 and the header means 248 involve the screen sections 206 and also successive tubular sections in the wall 269 separating the primary furnace chamber from the lower part of the secondary furnace chamber.

The side wall headers 274 for the lower part of the secondary furnace chamber are appropriately connected by circulators 276 and the wall tubes extending upwardly from these headers as well as the several furnace wall tubes below the level 210210 are preferably covered with high temperature refractory material thermally and mechanically maintained thereon by metallic studs secured to the tubes in good heat transfer relationship and extending into the refractory material in the manner indicated in the patent to Bailey 2,239,662 of April 22, 1941.

, Others of the tubes leading directly upward from the lowermost header 246 include the wall tube sections 270 disposed along the wall 272, and similar side wall steam generating tubes such as 273 lead upwardly from side wall headers 274 disposed at opposite sides of the unit. Such side wall steam generating tubes have their upper ends connected to the header means, such as that indicated at 249. The above described parts of the FIGURE 4 unit may be considered as involving the saturated system inasmuch as the tubes of these parts are steam generating tubes of a natural circulation system and are supplied with an excess of water from the water space of the drum 254.

The unit shown in FIGS. 4 to 8 inclusive has two separate steam superheating systems, the component tubes of which are subject to heat absorption from the gases in the unit. Referring particularly to FIG. 5 the low pressure steam superheating circuit or system receives steam at a pressure of 350 p.s.i. at the inlet of the low pressure heat exchangers 280 and 282, while the similar heat exchangers 284 and 286 constitute the initial parts of the high pressure steam superheating system, receiving steam at a pressure of the order of 600 p.s.i.a. These heat exchangers are each similar to that shown in FIG. 1 and referred to in the pertinent description. Each is constructed to handle I the 2400 p.s.i.a. steam from the drum 254, and each has an inlet similar to the inlet indicated at 10 in FIG. 1. The inlets for the heat exchangers 284 and 286 receive the high pressure steam for flow through the central annular chamber of the heat exchanger and then around and between the tubes 290 conducting the 2400 p.s.i.a. steam from its inlet chamber 292 to its intermediate chamber 294, and thence to the outlet chamber 296. The condensate from the high pressure steam formed as a result of the heat absorption involved in the superheating of the lower pressure steam passes from the chamber 296 through one or more recirculators 298 back to the drum 254. The inlet chamber 292 for the 2400 p.s.i.a. steam receives steam through one or more conduits or circulators 300.

The upper parts of the unit indicated in FIG. 4 of the 'drawings involve the components of the superheating system for the 600 p.s.i.a. steam, and to keep the separate systems for the 600 p.s.i.a. steam and the 350 p.s.i.a. steam separate, Roman numerals will be used herein to trace the flow of the 600 p.s.i.a. steam through the superheating components indicated in FIG. 4, and letters will be used to trace the fiow of the 350 p.s.i.a. steam in FIG. 7.

The heat exchanger indicated in FIG. 4 of the drawings may be considered as the heat exchanger 284 of FIG. 5, or otherwise indicated as the initial part I of the 600 7 p.s.i.a. steam superheating system. Tracing the flow of steam therefrom, it flows from the central chamber of the heat exchanger 284 through one or more conduits II leading to the intermediate superheater header III. This header extends entirely across the unit as indicated in FIG. 8 of the drawings. From this header steam flows through a row of tubes, the first sections 302 of which extend along the roof of the rearward portion 228 of the horizontal gas pass at the upper part of the unit. The flow then continues through the upright and widely spaced screen sections 304 and 306 between which the heating gases exit from the horizontal gas pass 228 and then flow past the dampers 308 into the flue 310 leading to the air heater 312.

From the upright screen sections 304 and 306 the steam flows through the gas pass floor tube sections 314 to the header IV. From this header the steam flows through a series of connecting tubes such as 316 to the side wall header V, there being such a header at each side of the unit with it own separate series of connecting tubes, such as 316. Leading upwardly from the header V is a row of superheater wall tubes 320 included in the side wall of the horizontal gas pass 228. The upper and outlet ends of these tubes are connected to discharge into the side wall header, VI, it being understood that there is a row of tubes 320 along each wall of the gas pass leading to separate headers such as the headers VI. From these headers the steam passes through the connecting tubes indicated at 324-326 to the header VII.

From the header VII, the steam flows downwardly through the inlet tubular sections 330 through serially connected return bend tubes constituting the banks 332 and 334 of convection superheater tubes, the outlet sections of which are in communication with the header VIII.

From the header VIII the steam fiows downwardly through one or more conduits 338 to the header means indicated at IX. As previously described this header means may include sections along the four sides of the furnace chamber 208. From these sections the steam flows upwardly through the radiant superheater wall tubes included in the walls of the furnace chamber 208, some of these tubes being indicated at 220 and 222. The flow of steam continues through these tubes to the header X, from which the steam flows, as indicated by the arrows 342 and 344 through the connecting tubes 346 to the header XI.

Steam flowing upwardly through the wall tubes 348 along the side walls of the furnace chamber 208 enters the side wall headers 350 and then flows as indicated by the arrow 352 (FIG. 4) to the header XI, through the connecting tubes 354. From the header XI, steam flows through a multiplicity of serially connected return bend tubes forming the banks of secondary superheater tubes 360-362. The outlet ends of these tubes are connected to the header XII, from which the highly heated superheated steam fiows through one or more conduits 366 to a steam turbine, or other appropriate point of use.

Turning now to the flow of low pressure (350 p.s.i.a.) steam from the low pressure source, it is understood that the initial parts of the circuits or systems for the low pressure steam fiow are the parts A which are formed by the heat exchangers 280 and 282 as they are illustrated in FIG. 5 of the drawings. This 350 p.s.i.a. steam enters the inlet 400 (FIG. 7) of the heat exchanger 280 and then flows from the central circular chamber of that heat exchanger through one or more conduits 402 to the header B, which is illustrated in FIG. 8 of the drawings as extending throughout the width of the gas pass 404 which is separated by a wall 406 from the gas pass 408 in which the banks of tubes 332 and 334 for the 600 p.s.i.a. steam superheater are disposed.

The low pressure (350 p.s.i.a.) steam flows from the header B (FIG. 7) through serially connected return bend tubes forming the banks 410 and 412 of convection superheater tubes. These tubes have their outlet ends connected to the header C from which the superheated low pressure steam fiows through one or more conduits 414 to an intermediate stage of a multi-stage steam turbine, or to other appropriate point of use.

The superheater headers above the furnace chamber 208 and above the horizontal gas pass 228, and the tubular connections between those headers are enclosed within a casing which is preferably gas tight and which is constructed of such material that it forms the thermal insulation. This casing is indicated in FIGS. 1 and 4 as having a roof section 430, a rear wall section 432, drum enclosing sections 434 and 436, front and rear wall sections 438 and 440, the section 442 at the base of the horizontal gas pass, and other sections 444-446 about the lower part of the unit including the cyclone furnace 220 and the primary furnace chamber 204. It is understood that similar casing sections are disposed along the side walls of the unit.

The casing sections of the unit are supported from the pressure parts which are in turn, supported from steelwork including such elements as the columns indicated at and 192 in FIG. 1 and FIG. 4, and the top girders such as 194, 196, and 198. The pressure units, such as the drum, the headers and the tubes are supported in a manner well known in the art from the upper part of the steelwork by means of hangers and drum straps.

Referring again to the low pressure (350 p.s.i.a.) steam superheating system indicated in FIG. 7 of the drawings, the heat exchanger 280 has its inlet chamber connected by a conduit 450 leading from the drum 254 for the fiow of 2400 p.s.i.a. steam to the heat exchanger in the same manner as that referred to in connection with the description of FIGS. 1 and 4, condensate from'the superheating effect within the heat exchanger 280 flowing from the 2400 p.s.i.a. outlet chamber of the heat exchanger back to the water space of the drum 254 through one or more conduits 452.

Referring to FIG. 6 of the drawings, and with more particular reference to FIG. 4, the heated air outlet 454 of the air heater 312 is connected to secondary air conduits 456 and 458 having the venturi sections 460 and 462. These conduits lead to the air inlets of the cyclones 200 by connecting ductwork such as indicated at 464 and 466.

FIGURE 6 also indicates that the dampers 308 are provided across the outlet of the sub-gas pass for the high pressure convection superheater formed by the banks of tubes 332 and 334. Similar dampers 470 are disposed across the outlet of the sub-gas pass for the low pressure convection superheater formed by the banks of tubes 410 and 412. By appropriate control of these dampers the total gas flow may be proportioned between the two gas passes.

Whereas the invention has been described with reference to the details of a particular unit as set forth in the associated drawings, it is to be realized that the invention is not to be considered as limited to all of the details of that preferred embodiment. Various combinations of the main components of the invention may he obviously used with variations of other associated components, within the scope of the subjoined claims.

What is claimed is:

1. In an apparatus of the character described; a high pressure steam generator including a vertically elongated fuel fired furnace having upright steam generating tubes along its walls, a steam and water drum at the upper part of the high pressure steam generating unit receiving the steam generated in said wall tubes, contiguously arranged and horizontally disposed radiant superheater tubes of a second superheating stage constituting parts of the walls of gas confining enclosure leading from the upper part of the furnace, banks of successive upright and horizontally spaced superheater tubes constituting a convection heated section of a second superheating stage and arranged transversely of gas flow in said gas pass, independent sources of low pressure steam at substantially different pressures; separate steam superheating circuits for the steam of said different pressures and a first stage of superheating constituted by an indirect heat exchanger for each of said circuits; means for conducting low pressure steam from said independent sources through the first superheating stages; means for conducting high pressure steam from the steam and water drum for effecting indirect heat transfer to the low pressure steam in the first superheating stages by condensing the high pressure steam; means for returning condensate from the first superheating stages to the liquid space of the high pressure steam generating means, and means for conducting the superheated steam from the first superheating stages to and through the tubular components constituting second superheating stages for the different circuits and also constituting a unitary part of the unit in which the high pressure steam is generated.

2. In apparatus of the character described; a high pressure steam generator including a vertically elongated fuel fired furnace having upright steam generating tubes along at least the lower portions of its walls, a steam and water drum at the upper part of the high pressure steam generating unit receiving the steam generated in said wall tubes, contiguously arranged and horizontally disposed radiant superheater tubes of a second superheating stage constituting a portion of the walls of said furnace and parts of the walls of a gas confining enclosure leading from the upper part of the furnace, banks of successive upright and horizontally spaced superheater tubes constituting a convection heated section of a second superheating stage and arranged transversely of gas flow in said gas pass, independent sources of low pressure steam at substantially different pressures; separate steam superheating circuits for the steam of said different pressures and a first stage of superheating constituted by an indirect heat exchanger for each of said circuits; means for conducting low pressure steam from said independent sources through the first superheating stages; means for conducting high pressure steam from the steam and water drum for effecting indirect heat transfer to the low pressure steam in the first superheating stages by condensing the high pressure steam; means for returning condensate from the first superheating stages to the liquid space of the high pressure steam generating means, and means for conducting the superheated steam from the first superheating stages to and through the tubular components constituting the separate second superheating stages for the different circuits and also constituting a unitary part of the unit in which the high pressure steam is generated.

References Cited in the file of this patent UNITED STATES PATENTS 753,433 Reeve Mar. 1, 1904 2,213,185 Armacost Sept. 3, 1940 2,291,195 Stieger July 28, 1942 2,424,476 Marshall July 22, 1947 2,708,656 Fermi et a1 May 17, 1955 

